A RAY REPRESENTATION OF SURFACE DIFFRACTION BY A MULTILAYER CYLINDER

Exact expressions are presented for the field produced by a point source radiating in the presence of an infinitely long multilayered cylindrical structure. The expressions are evaluated asymptotically for source and observation points that are widely removed from the cylinder surface and related so that the cylinder shadows the source from the observer. The diffracted field is interpreted in a ray-optic format. It is observed that surface-propagating waves along the layers can be slowed significantly as compared with those on an impenetrable cylinder of the same radius. This wave slowing requires that rays attaching to the cylinder refract into a layer-guided mode and refract a second time as the curved structure sheds energy into the scattered field. Consequently, rays attaching to and shedding from the cylinder are not tangent to it when the layer profile slows the surface-propagating waves. The analysis applies for both metallically backed and open-shell layers. Computed diffraction coefficient results are given for a coated metallic cylinder as a function of coating thickness.